Smart cities will rely on low-power sensors embedded in many devices and structures (Credit: Shutterstock)

Researchers have claimed a “major step” in the accelerating spread of the Internet of Things (IoT), creating a low-cost, battery-free ‘wake-up timer’ to make sensor power consumption 1,000 times lower than previously possible.

The timer, built to trigger sensors to perform their tasks when needed, is reportedly so efficient that it runs using an on-chip solar cell with a diameter close to that of a human hair. It was created by researchers from the Green IC group at the National University of Singapore (NUS) in collaboration with associate professor Paolo Crovetti from the Polytechnic University of Turin in Italy.

The IoT is increasingly prevalent in consumer applications, monitoring and connecting growing numbers of so-called ‘smart’ devices. It is also of increasing importance for many engineering sectors, with applications including optimisation and predictive maintenance of factory machines and stress monitoring of large structures such as bridges.

Connecting more structures and ‘smart city’ systems to the IoT will require extensive deployment of miniaturised silicon-chip sensors with very low power consumption and decades of battery lifetime. Sensor nodes include one or more sensors, as well as circuits for data processing, wireless communication and power management.

To keep power consumption low, nodes are kept in ‘sleep mode’ most of the time, and wake-up timers trigger them to switch on. As the timers themselves are turned on most of the time, they set the minimum power consumption of sensor nodes. They also play a fundamental role in reducing their average power consumption.

The new wake-up timer is an on-chip circuit capable of running on picowatt-scale power, equivalent to one billion times lower than a smartwatch. It does not require additional circuitry such as voltage regulators, which drastically increase power consumption, thanks to a reduced sensitivity to supply voltage.

“Under typical office lighting, our novel wake-up timer can be powered by a very small on-chip solar cell that has a diameter similar to that of a strand of human hair. It can also be sustained by a millimetre-scale battery for decades,” said the research team leader, associate professor Massimo Alioto. “This is a major step towards accelerating the development of IoT infrastructure, and paves the way for the aggressive miniaturisation of IoT devices for long-lasting operations.”

The wake-up timer can continue operations even when a battery is not available and with very little ambient power, as demonstrated by a miniaturised on-chip solar cell exposed to moonlight. An on-chip capacitor used for slow and infrequent wake-up also helps reduce the device’s silicon manufacturing cost thanks to its small surface area of 49 microns on both sides.

“Overall, this breakthrough is achieved through system-level simplicity via circuit innovation,” said researcher Dr Orazio Aiello. “We have demonstrated silicon chips with substantially lower power that will define the profile of next-generation IoT nodes. This will contribute towards realising the ultimate vision of inexpensive, millimetre-scale and, eventually, battery-less sensor nodes.”

The work was presented at the 2018 Symposia on VLSI Technology and Circuits in Honolulu, Hawaii.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.